Various types of variable speed transmission and drive mechanisms have been proposed where a pair of cone-shaped pulleys or rollers are mounted on parallel axes, with the apex of the cones or frusto-conical shaped rollers being oppositely directed. A belt is entrained about each cone or roller and may be positioned laterally in order to achieve varying drive ratios. These prior art devices have usually been difficult to assemble and adjust and numerous operations and parts were required to assemble and operate the drive unit, in order to provide the proper tension for the endless belt entrained over the rollers. Furthermore, the prior art devices were expensive to fabricate, particularly the cones or the tapered rollers and were not sufficiently simple in construction and compact in size so as to enable their use in restricted areas.
Assemblies of such prior art devices are shown in the United States Pat. No. 2,638,008 issued May 12, 1953 which has shifter wheels that force the belt onto the cones for good contact; and U.S. Pat. No. 2,734,391 which issued Feb. 14, 1956 and which employs an electromagnetic shifter for shifting the endless belt along the length of tapered rollers.